The spectral content of electromagnetic waves reflected off of, or emitted from, a target provides information about the properties of that target. In some circumstances, the spectral content of the electromagnetic waves reflected off of, or emitted from, a target provides information about the chemical composition of the target. Based on the information provided by the reflected and/or emitted electromagnetic waves, the target can be classified. For example, the target's composition may be determined. In cases where the target is vegetation, it may be possible to determine a condition of the vegetation.
Multi-spectral imaging (MSI) and hyperspectral imaging (HSI) systems, which are capable of capturing incident light as a function of spectral wavelength, may be used to collect such information about a target for a large variety of applications.
The electromagnetic waves that are reflected off of a target are from a light source. Therefore, the spectral content of the electromagnetic waves reflected off of a target will also be a product of the electromagnetic waves provided by the light source. Different light sources and different conditions affecting a light source will cause the spectral content of the electromagnetic waves from the light source to differ. Therefore, it is necessary to provide systems and methods to calibrate the spectral content measurements captured of the target.
Calibration systems have been used whereby the target is illuminated by an artificial light source having a known spectral content. Calibration systems have been used whereby a target calibration panel having a known spectral reflectance has been placed in the field of view of the target spectral measurement devices and used to calibrate the target spectral measurements. Calibration systems have also been used which measure the spectral content of the light sources directly.